Impact wrenches of the above type are previously described in for instance U.S. Pat. No. 3,648,784 and U.S. Pat. No. 3,661,217.
A problem related to impact wrenches of the above described type is mechanical wear and a limited service life due to poor lubrication of the parts of the impact mechanism. Lubricant in the form of grease that is applied at the assemblage of the impact mechanism, and also supplied after some intervals of use, tends not to stay within the impact mechanism but is expelled from the rotating drive member and is deposited on the inside walls of the wrench housing. Grease gathered on the inside walls of the housing is of no use but could instead, if gathered in a too large quantity, cause a braking effect on the drive member and, hence, a reduction in power output of the impact wrench.